1. Field of the Invention
This invention relates broadly to thin film diamond coatings. More particularly, this invention relates to the use of a thin film diamond coating as a protectant against corrosion and erosion in semiconductor processing chambers.
2. State of the Art
One step in the manufacture of semiconductor chips is processing a wafer in a semiconductor processing chamber to deposit layers on the wafer. The process of depositing layers on a semiconductor wafer substrate usually involves a chemical vapor deposition (CVD) or physical vapor deposition (PVD )process in which the wafer is placed on a graphite mandrel (which may also be designed as a susceptor for microwave or other radiation) in a thermal reactor chamber. The mandrel is typically coated with silicon carbide (SiC) to protect the graphite against corrosion. As used herein, the term xe2x80x9ccorrosionxe2x80x9d refers to physical and/or chemical degradation. The wafer is held within a stream of a reactant gas flowing across the surface of the wafer. The thermal reactor may be heated to a high temperature by external lamps which pass infra-red radiation into the reactor chamber through heating ports. The heating ports are typically positioned both above and below the mandrel, and are covered by quartz windows which are transparent to the infra-red radiation. The mandrel positions and rotates the wafer during the deposition process, and a pyrometer aimed at the back of the mandrel is generally used to detect the temperature of the mandrel, and thereby the wafer, during processing and to serve as an input to a controller for the power to the external lamps.
During the process, the interior surfaces of the chamber and surfaces of components within the chamber are subject to coating by a deposition film. For example, during a high temperature nitride process, silicon nitride ceramic film is deposited on the walls of the chamber as well as the mandrel. As the deposition film on the chamber walls and mandrel thickens, it is prone to flaking, which introduces undesirable particulates into the chamber as well as alters the radiation emissivity of the mandrel. As the emissivity of the mandrel changes, the accuracy of a pyrometer coupled to the mandrel to monitor the temperature of the mandrel is compromised. As a result, the precision of controlling the temperature of the mandrel and consequently the precision of depositing the deposition film on the mandrel becomes limited.
Therefore, an in-situ etching process is periodically used to remove the ceramic film from the chamber walls, the mandrel, and other coated surfaces. Typically, a halogen gas or plasma, e.g., NF3, is used as the etchant. It is not uncommon for portions of a protective coating on the mandrel to also be etched away during this process, and once the protective coating is removed from the surface of the mandrel, the mandrel itself is subject to corrosive attack by the etchant. Other surfaces of the system are similarly effected. Attack by the etchant affects the emissivity of the mandrel which, discussed above, reduces quality control over the semiconductor wafer. Moreover, such etching reduces the structural integrity of the etched system components.
It is known that a thick film CVD diamond, e.g., 200-300 microns thick, is an effective protective coating against both mechanical and chemical degradation. However, as a practical matter the cost of such thick diamond films prohibits their use in this application.
U.S. Pat. No. 5,916,370 to Chang discloses using relatively thin diamond films, e.g. 7-15 microns thick, to protect against corrosion and erosion in semiconductor processing chambers. However, thin diamond films are generally not nearly as effective a protective coating as are thick diamond coatings. The processing chamber corrosion is a particularly challenging problem and attacks even materials coated with the diamond film described in Chang.
Similar problems exist for materials in other environments subject to highly corrosive fluids.
In accordance with the present invention, a novel combination of a member coated with a thin film diamond coating formed by a particular process has been determined to be as effective in resisting corrosion as is a typical CVD diamond thick film. The thin film diamond coating is formed relatively slowly with a relatively low methane concentration and is identified by its Raman spectrographic characteristics. The thin film diamond, preferably 5 to 40 microns thick, has substantially similar Raman characteristics to the thick film diamond disclosed in U.S. Pat. No. 5,736,252 to Bigelow et al., which is hereby incorporated by reference herein in its entirety. While the Bigelow et al. patent identified that the thick free standing diamond film described therein had particular favorable thermal conductivity and optical transparency, it was not recognized that a thin film diamond grown in the described manner and having the resulting particular Raman spectrographic characteristics would provide substantially greater corrosion resistance in a corrosive environment and greater erosion resistance in a mechanically degrading environment than other thin film diamond coatings. It is believed that such a thin film diamond coating is provided with enhanced chemical resistance and mechanical integrity due to its purity and quality. In particular, the process minimizes grain boundaries where impurities tend to concentrate and which present an opportunity for free chemical bonds to be available at the surface. Exposed grain boundaries are therefore generally more susceptible to chemical activity and mechanical breakdown than exposed bare crystalline surfaces.
According to one embodiment of the invention, the particularly specified thin film diamond coating is coated onto exposed surfaces within a semiconductor processing chamber. The exposed surfaces of the processing chamber are thereby provided with a protective coating which resists mechanical and chemical degradation, and which is particularly resistive to chemical attack at a variety of temperatures.
According to another embodiment of the invention, in an environment in which various fluids containing corrosive environmentally harmful constituents are to be detoxified by electrolytic means, electrodes are coated with the specified diamond coating. The electrodes may be made conductive by adding to the diamond of the coating an electrical charge carrier dopant, e.g. boron, to increase its electrical conductivity. The dopant may be a donor or acceptor type.
Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures.